<html>
<head>
<script>
function makeDeeper() {
  // Create an about:blank iframe nested inside the existing #f1 about:blank
  // iframe.
  var iframe = document.getElementById("f1");
  var grandKid = iframe.contentDocument.createElement("iframe");
  iframe.contentDocument.body.appendChild(grandKid);
}
</script>
</head>
<body onload="makeDeeper()">
  <p>This page has an iframe. Yay for iframes!
  <p><iframe src="about:blank" id="f1"></iframe>
</body>
</html>
